Field of the Invention
The present invention relates generally to an evaporative type cooling system for an internal combustion engine wherein liquid cooling is permitted to boil and the vapor used as a vehicle for removing heat therefrom, and more specifically to such a system which does not require a plurality of electromagnetic valves and a complex control circuit to ensure that the system remains free of contaminating non-condensible matter and which can control the boiling point of the coolant in accordance with the instant mode of engine operation.
Description of the Prior Art
In currently used "water cooled" internal combustion engines (liquid) is forcefully circulated by a water pump, through a cooling circuit including the engine coolant jacket and an air cooled radiator. This type of system encounters the drawback that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat.
Further, due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having an 1800 cc displacement (by way of example) is operated full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this, a flow rate of 167 liter/min (viz., 4000-60.times.14) must be produced by the water pump. This of course undesirably consumes several horsepower. Further, the large amount of coolant utilized in this type of system renders the possibility of quickly changing the temperature of the coolant in a manner that instant coolant temperature can be matched with the instant set of engine operational conditions such as load and engine speed, completely out of the question.
FIG. 2 shows an arrangement disclosed in Japanese Patent Application Second Provisional Publication Sho. No. 57-57608. This arrangement has attempted to vaporize a liquid coolant and use the gaseous form thereof as a vehicle for removing heat from the engine. In this system the radiator 1 and the coolant jacket 2 are in constant and free communication via conduits 3, 4 whereby the coolant which condenses in the radiator 1 is returned to the coolant jacket 2 little by little under the influence of gravity. This arrangement while eliminating the power consuming coolant circulation pump which plagues the above mentioned arrangement, has suffered from the drawbacks that the radiator, depending on its position with respect to the engine proper, tends to be at least partially filled with liquid coolant. This greatly reduces the surface area via which the gaseous coolant (for example steam) can effectively release its latent heat of vaporization and accordingly condense, and thus has lacked any notable improvement in cooling efficiency. Further, with this system in order to maintain the pressure within the coolant jacket and radiator at atmospheric level, a gas permeable water shedding filter 5 is arranged as shown, to permit the entry of air into and out of the system.
However, this filter permits gaseous coolant to readily escape from the system, inducing the need for frequent topping up of the coolant level. A further problem with this arrangement has come in that some of the air, which is sucked into the cooling system as the engine cools, tends to dissolve in the water, whereby upon start up of the engine, the dissolved air tends to come out of solution and forms small bubbles in the radiator which adhere to the walls thereof and form an insulating layer. The undissolved air also tends to collect in the upper section of the radiator and inhibit the convection-like circulation of the vapor from the cylinder block to the radiator. This of course further deteriorates the performance of the device.
European Patent Application Provisional Publication No. 0 059 423 published on Sept. 8, 1982 discloses another arrangement wherein, liquid coolant in the coolant jacket of the engine, is not forcefully circulated therein and permitted to absorb heat to the point of boiling. The gaseous coolant thus generated is adiabatically compressed in a compressor so as to raise the temperature and pressure thereof and thereafter introduced into a heat exchanger (radiator). After condensing, the coolant is temporarily stored in a reservoir and recycled back into the coolant jacket via a flow control valve. This arrangement has suffered from the drawback that when the engine is stopped and cools down the coolant vapor condenses and induces sub-atmospheric conditions which tend to induce air to leak into the system. This air tends to be forced by the compressor along with the gaseous coolant into the radiator.
Due to the difference in specific gravity, the above mentioned air tends to rise in the hot environment while the coolant which has condensed moves downwardly. The air, due to this inherent tendency to rise, tends to form pockets of air which cause a kind of "embolism" in the radiator and which badly impair the heat exchange ability thereof. With this arrangement the provision of the compressor renders the control of the pressure prevailing in the cooling circuit for the purpose of varying the coolant boiling point with load and/or engine speed difficult.
U.S. Pat. No. 4,367,699 issued on Jan. 11, 1983 in the name of Evans (see FIG. 3 of the drawings) discloses an engine system wherein the coolant is boiled and the vapor used to remove heat from the engine. This arrangement features a separation tank 6 wherein gaseous and liquid coolant are initially separated. The liquid coolant is fed back to the cylinder block 7 under the influence of gravity while the relatively dry gaseous coolant (steam for example) is condensed in a fan cooled radiator 8.
The temperature of the radiator is controlled by selective energizations of the fan 9 which maintains a rate of condensation therein sufficient to provide a liquid seal at the bottom of the device.
Condensate discharged from the radiator via the above mentioned liquid seal is collected in a small reservoir-like arrangement 10 and pumped back up to the separation tank via a small constantly energized pump 11.
This arrangement, while providing an arrangement via which air can be initially purged to some degree from the system tends to, due to the nature of the arrangement which permits said initial non-condensible matter to be forced out of the system, suffers from rapid loss of coolant when operated at relatively high altitudes. Further, once the engine cools air is relatively freely admitted back into the system. The provision of the bulky separation tank 6 also renders engine layout difficult.
Further, the rate of condensation in the condensor is controlled by a temperature sensor disposed on or in the condensor per se in a manner which holds the pressure and temperature within the system essentially constant. Accordingly, temperature variation with load is rendered impossible.
Japanese Patent Application First Provisional Publication No. sho. 56-32026 (see FIG. 4 of the drawings) discloses an arrangement wherein the structure defining the cylinder head and cylinder liners are covered in a porous layer of ceramic material 12 and wherein coolant is sprayed into the cylinder block from shower-like arrangements 13 located above the cylinder heads 14. The interior of the coolant jacket defined within the engine proper is essentially filled with gaseous coolant during engine operation.
However, this arrangement has proved totally unsatisfactory in that upon boiling of the liquid coolant absorbed into the ceramic layers, the vapor thus produced and which escapes toward and into the coolant jacket, inhibits the penetration of fresh liquid coolant into the layers and induces the situation wherein rapid overheat and thermal damage of the ceramic layers 12 and/or engine soon results. Further, this arrangement is of the closed circuit type and is plagued with air contamination and blockages in the radiator similar to the compressor equipped arrangement discussed above.
FIG. 5 shows an evaporation type cooling system disclosed in Japense Patent Application Second Provisional Publication No. 47-5019. This arrangement is such that when the coolant in the coolant jacket 15 heats and expands the excess coolant is displaced from the top of the radiator 16 to a reservoir 17 via a discharge conduit 18. This conduit, as shown, extends into the reservoir 17 and terminates close to the bottom thereof. With this arrangement when coolant vapor is discharged from the radiator 16 it bubbles through the liquid coolant in the reservoir 17 and condenses. A cooling fan 19 is arranged to induce a cooling draft of air to pass over the finned tubing of the radiator and induce coolant vapor to condense. Depending on the ambient temperature and the amount of heat being produced by the engine the level of liquid coolant reduces under the boiling action until an equilibrium level is established.
When the engine stops and cools, coolant from the reservoir 18 is re-inducted to fill the radiator 16 and coolant jacket 18. The chamber 20 which is fluidly communicated with the bottom of the reservoir acts as a gas spring.
However, with this arrangement as the system is hermetically sealed control of the boiling point of the coolant using only the fan is extremely difficult.
FIG. 8 shows an arrangement which is disclosed in U.S. Pat. No. 4,549,505 issued on Oct. 29, 1985 in the name of Hirano. The disclosure of this application is hereby incorporated by reference thereto. For convenience the same numerals as used in the above mentioned Patent are also used in FIG. 8.
However, this arrangement while solving the drawbacks encountered with the previously disclosed prior art has itself suffered from the drawbacks that a plurality of electromagnetic valves and conduits are required to enable the desired temperature and coolant control. This adds to the cost and complexity of the system as well as increasing the crowding of the engine compartment when used in conjunction with an automotive engine.